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The thyroid gland actively takes up iodine and incorporates iodine into thyroid hormone. Hence iodine deficiency or iodine excess can affect thyroid function, and produce thyroid disease. In some parts of the world, iodine deficiency remains a public health problem, and may lead to endemic goiter, hypothyroidism, and problems with optimal mental development. Accordingly, many countries have adopted widespread iodine supplementation programs as part of their approach to public health. For an overview of this type of program, see Drug Saf 2000 Feb;22(2):89-95 Iodine supplementation: benefits outweigh risks. If a patient with thyroid disease does not have adequate exposure to iodine in their diets or environment, then iodine supplementation may be helpful.

Most regions of North America have adequate exposure to iodine in the diet. For example, review the results of a survey of iodine levels in the US population Iodine status of the U.S. population, National Health and Nutrition Examination Survey 2003-2004 Thyroid. 2008 Nov;18(11):1207-14. Hence additional supplementation with exogenous iodine, or iodine-rich foods such as kelp, may sometimes produce or exacerbate thyroid disease. Following implementation of an iodine supplementation regimen, there is a shift in the epidemiology of specific thyroid diseases, as reviewed in Thyroid 1998 Dec;8(12):1179-83 Epidemiology of thyroid diseases in iodine sufficiency. Indeed, several epidemics of iodine-induced thyroid dysfunction have been described that follow iodine supplementation programs, as reviewed in Thyroid 1998 Jan;8(1):83-100 Iodine-induced hyperthyroidism: occurrence and epidemiology and increases in the rates of hypothyroidism have been described in iodine-supplemented populations. See Large Differences in Incidences of Overt Hyper- and Hypothyroidism Associated with a Small Difference in Iodine Intake: A Prospective Comparative Register-Based Population Survey. J Clin Endocrinol Metab. 2002 Oct 1;87(10):4462-4469.

Furthermore, in the absence of supplementation, excess iodine intake in different populations has also been associated with an increased incidence of goiter and thyroid dysfunction. See Endemic goiter associated with high iodine intake Am J Public Health 2000 Oct;90(10):1633-5. 

Patients in North America may be exposed to excess iodine through dietary supplements, drugs such as amiodarone (Cordarone), cough and cold remedies, or foods such as kelp and various preparations containing seaweed extracts. It is important to be aware of potential sources of iodine excess, as this may influence the results of thyroid function testing, including interpretation of blood tests and nuclear medicine studies such as the thyroid scan or iodine uptake.

In some clinical settings, patients with severe hyperthyroidism may actually be treated with iodine for several days, which can also act paradoxically to transiently suppress release of thyroid hormone.

Iodine supplementation to patients with small goiters who live in parts of the world not characterized by iodine deficiency may exacerbate or unmask autoimmune thyroid disease. See The effect of iodine administration on the development of thyroid autoimmunity in patients with nontoxic goiter Thyroid 2000 Jun;10(6):493-7.

Although many patients are under the assumption that taking kelp, or iodine supplements will improve their thyroid function, it is quite common, particularly in older individuals, for iodine supplementation to paradoxically result in the development of hyperthyroidism. See Iodine-induced hyperthyroidism: occurrence and epidemiology. Thyroid. 1998 Jan;8(1):83-100. Review.

To review the use of iodine-containing supplements for the treatment of hyperthyroidism, or the development of hypothyroidism following exposure to iodine, see Iodine-Induced hypothyroidism. Thyroid. 2001 May;11(5):501-10.

To review the development of hyperthyroidism following exposure to iodine, see Iodine excess and hyperthyroidism. Thyroid. 2001 May;11(5):493-500.


How much iodine should I take to prevent my thyroid being exposed to radioactive iodine during a nuclear medicine test or after a nuclear accident?

Some patients will be prescribed drops of saturated iodine or Lugol's iodine, whereas others will take iodine in tablet form. A dose of about 100 mg daily will block the majority of exogenous iodine uptake in most patients. See Iodine kinetics and effectiveness of stable iodine prophylaxis after intake of radioactive iodine: a review. Thyroid. 2001 Apr;11(4):353-60.

To review specific recommendations about major radiation exposure see N Engl J Med 2002 May 16;346(20):1554-61, as excerpted below:

In the event of the detonation of a nuclear weapon or the release of radioactive material from a nuclear reactor, the most likely treatment of internal contamination would be the use of potassium iodide or iodate to prevent radioiodine from accumulating in the thyroid. The recommended daily dose of potassium iodide is 130 mg for adults, 65 mg for children 3 to 18 years old, 32 mg for children 1 month to up to 3 years old, and 16 mg for infants less than 1 month old. Potassium iodide must be taken shortly before exposure or within several hours after exposure to be effective. Both the Nuclear Regulatory Commission and the FDA have approved the use of potassium iodide in emergencies. Potassium iodide is widely available through the mail and the Internet. Too high a dose will result in iodism, but the risk of serious side effects with the recommended dose is extremely small. Chelating agents (calcium or zinc diethylenetriamine pentaacetic acid) are investigational drugs and are useful only if there is direct dispersal of plutonium or americium. Such agents are not very useful for the treatment of contamination with other radionuclides, and they are not useful after the detonation of a nuclear weapon.

I am scheduled to receive radioactive iodine as part of my thyroid cancer treatment. Should I follow a low iodine diet?

Although some physicians routinely prescribe a low iodine diet prior to administration of therapeutic dose of radioactive iodine, there have been no randomized control trials demonstrating the benefits of such diets. Furthermore, as many different types of foods contain iodine, it can be very challenging to follow a low iodine diet. Discuss this issue with your physician on an individual basis.

What should I do about my jewelry during my radioactive iodine treatment?

 Although the risk of contaminating jewelry with radioactive iodine is small, this can rarely happen. Hence, wherever possible, it is probably prudent to leave your jewelry at home. See Contamination of a bracelet following iodine-131 therapy: a case report. J Nucl Med Technol. 2000 Dec;28(4):257-8.